The present invention relates to an axle assembly for a vehicle suspension system. In vehicle suspension systems, it is often desirable to provide a relatively high roll stiffness so that the attitude of the vehicle remains relatively stable during cornering, and a relatively low articulation stiffness so that as the vehicle traverses uneven terrain wheels of the vehicle are permitted to articulate and thereby substantially maintain equal loading on the wheels. This is especially important for vehicles which have high roll moments, such vehicles including most all-wheel drive off-road vehicles and all trucks. It is common to provide each set of wheels of a truck with a suspension system which includes an axle assembly having an elongate axle member extending substantially transversely of the truck and at least two elongate trailing arms connected at their ends to respective spaced locations on the axle member so as to form a substantially C shaped rigid member. In use, ends of the trailing arms remote from the axle member are flexibly connected to an underside portion of a chassis of the truck and a pair of wheels are rotatably mounted on the axle member. The purpose of such a suspension system is to provide each axle member of the truck with a relatively high roll stiffness, roll of the vehicle being resisted by virtue of the torsional and bending resistance of the axle member and the trailing arms.
Although the above described suspension system operates satisfactorily in reducing roll of the vehicle, a consequence of rigidly coupling together the trailing arms and the axle member is that they provide resistance to all rotations of the axle member about a longitudinal axis of the vehicle body. This prevents the cross-axle articulation stiffness of the vehicle axle members from being decoupled from the high roll stiffness provided by the axle members and their corresponding trailing arms. In addition, where the road surface is uneven, unnecessarily high wheel loads are generated which cause degradation of the road surface.
The present invention seeks, among other things, to overcome the above mentioned disadvantages.
In accordance with an alternative aspect of the present invention, there is provided an axle assembly for a suspension system of a vehicle, said assembly including an elongate axle member adapted to rotatably receive wheels of a vehicle, a first arm member operatively associated with said axle member and flexibly connected, in use, to a chassis of said vehicle, a second arm member operatively associated with said axle member and flexibly connected, in use, to a chassis of said vehicle, and first ram means operatively associated with the first arm member and said axle member, the arrangement being such that when expansion or contraction of the first ram means is restricted, rotation of said axle member relative to the first arm member is restricted, and when expansion or contraction of the first ram means is permitted, rotation of said axle member relative to the first arm member is permitted.
In this way, by controlling the freedom of movement of the first and second ends of the ram means towards or away from each other, the desired roll stiffness and articulation stiffness can be obtained.
In accordance with an aspect of the present invention, there is provided an axle assembly for a suspension system of a vehicle, said assembly including an elongate axle member adapted to rotatably receive wheels of a vehicle, a first arm member operatively associated with said axle member and flexibly connected, in use, to a chassis of said vehicle, and first ram means operatively associated with the first arm member and said axle member, the arrangement being such that when expansion or contraction of the first ram means is restricted, rotation of said axle member relative to the first arm member is restricted, and when expansion or contraction of the first ram means is permitted, rotation of said axle member relative to the first arm member is permitted.
In accordance with a further alternative aspect of the present invention, there is provided a suspension system including a first vehicle support means including an axle assembly as described above in relation to an aspect of the present invention, and a second vehicle support means having third ram means, said third ram means being operatively associated with at least said first ram means and said second vehicle support means being configured such that the first vehicle support means and the second vehicle support means cooperate with each other so that roll of said vehicle is resisted and articulation of said vehicle is substantially permitted.